1. Field of the Invention
The present invention relates to a brake apparatus for a linear motor, which is used for positioning a movable section of the linear motor with respect to a fixed section of the linear motor, and to a method for positioning the movable section.
2. Description of the Related Art
A linear motor comprises a coil arranged on any one of a movable section and a fixed section thereof, and as necessary, a permanent magnet is arranged on the other of the movable section and the fixed section, so that the permanent magnet is opposed to the coil. The movable section is displaced with respect to the fixed section by means of a thrusting force, which is generated on the basis of Fleming's left hand rule when a current flows through the coil. In this arrangement, a brake apparatus is arranged for the movable section. When electric power supplied to the coil is halted, or when the movable section is displaced to a predetermined position, the movable section is positioned at a predetermined position with respect to the fixed section by actuating the brake apparatus (see Japanese Laid-Open Patent Publication Nos. 2000-184686 and 8-251904).
In the case of the brake apparatus disclosed in Japanese Laid-Open Patent Publication No. 2000-184686, an electromagnet and a brake pad are attached on a side portion of the movable member by means of a plate-shaped member, while a brake base, which is opposed to the electromagnet and brake pad, is arranged on a side portion of the fixed section opposed to the side portion of the movable section. In this arrangement, when electric power applied to the electromagnet is halted, the brake pad presses the brake base by an urging force of a coil spring, which is arranged between the electromagnet and the brake pad. Therefore, the movable section is positioned at a predetermined position with respect to the fixed section.
In the case of the brake apparatus disclosed in Japanese Laid-Open Patent Publication No. 8-251904, a plate-shaped member extends from a side portion of the movable section along a side portion of the fixed section. An electromagnet, which is opposed to the side portion of the fixed section, is arranged at a forward end of the plate-shaped member. With this arrangement, when electric power applied to the electromagnet is stopped, the electromagnet presses the side portion of the fixed section using a permanent magnet, and by means of an electromagnetic force resulting from a magnetic flux from the permanent magnet attached to the forward end of the electromagnet. As a result, the movable section is positioned at a predetermined position with respect to the fixed section.
Recently, for a linear motor, it is required that precise positioning be performed, for example, to an extent of not more than 1 μm. In order to achieve highly accurate positioning as described above, it is necessary that the movable section of the linear motor be correctly positioned with respect to the fixed section using a brake apparatus. For this purpose, backlash between the brake pad and the fixing member therefor must be decreased to be as small as possible, and further, backlash and positional deviation between the brake pad and the movable section should be suppressed to be as small as possible.
However, in the case of the brake apparatus disclosed in Japanese Laid-Open Patent Publication No. 2000-184686, play between the brake pad and the fixing member results in backlash, and it is impossible to position the movable section with respect to the fixed section at an accuracy of not more than 1 μm as described above. On the other hand, in the case of the brake apparatus disclosed in Japanese Laid-Open Patent Publication No. 8-251904, the plate spring for supporting the electromagnet is not rigidly secured, even though the electromagnet and the brake pad are integrated into one unit. Therefore, when the movable section is positioned with respect to the fixed section, it is impossible to avoid positional deviation of the movable section with respect to the brake apparatus. Further, in the case of the brake apparatuses disclosed in Japanese Laid-Open Patent Publication Nos. 2000-184686 and 8-251904, the brake pad is not rigidly secured. Therefore, a problem arises in that the movable section, once positioned, may undergo positional deviation due to deformations of the brake pad, even after the movable section has been positioned with respect to the fixed section.